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Composite design

Last modified by Iwona Budny Bjergø on 2022/01/24 11:01


Auto design of composite columns

The automatic design option is now also available for composite columns. It finds an optimal cross-section (within the predefined set of cross-sections ) with dimensions and applied reinforcement based on loads, internal forces and the requirements of the applied Eurocode standard.


The auto design algorithm works in the following way:

  1. It sorts the selected cross-sections according to their area.
  2. It tries to place and distribute the appropriate reinforcement for the calculations in cross section.
  3. If there is no suitable reinforcement arrangement for a cross-sectional size or type, or the ratio of longitudinal reinforcement exceeds the limit specified by the User, the following cross-sectional dimension or type shall be tested in accordance with step 2.

Note: Auto design works for columns with the cross-section types highlighted in blue.


Design parameters for auto design of composite columns


For each segment of each cross-section, the size of concrete cover can be specified.

Note: The reinforcement parameters of one cross-section type can be specified at a time.



Detailed geometry data and calculation details for the proposed cross-section and its reinforcement are available under the Utilization result of the given composite column.

composite-detailed result.png

Parametric reinforcement of composite columns

FEM-Design 21 provides a new way to manually define reinforcement of rectangular and circular composite columns with the most common reinforcement patterns. This is the same function that already exists for regular RC bars.


This option is also available in the graphic editor of Manual design.


Note: Applying parametric reinforcement deletes the existing ones.

Parametric reinforcement can be set for composite cross-sections with rectangular or circular shapes. And so, rectangular or circular reinforcement can be applied.


The following reinforcement parameters can be set at Default settings:

Identifier, position number and concrete covers


Stirrups' specification:


Longitudinal bars with different parameters for circular and rectangular cross-sections:


In case of a rectangular cross-section, one can choose from two predefined patterns for longitudinal bars: column-type or beam-type (characteristic for bending):




Fire design of composite columns

The use of concrete filled steel tubes (CHS/RHS/SHS) without fireproof coating is a common substitute for steel columns due to the expensive fire protection coating required for design. To support this design practice, fire design is now available for all composite column sections.


Eurocode 1994-1-2 offers three design approaches for member analysis of composite columns:

  • tabular data,
  • simple calculation models
  • and advanced computational model.

Unfortunately, none of them covers all the standard (and FEM-design-supported) composite cross-sections, and the standard even lacks guidance on advanced computational model. In order to support all cross-sections for which room design calculation is available, both tabular data and simplified calculation methods are implemented.

Read the full feature description at: Composite column fire design


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